Nico Rosberg will drive alongside Mark Webber at Williams next season after the 20-year-old German was named as the team's other driver for 2006.
Nico Rosberg is eager to avoid any comparison with his father
The GP2 champion, son of 1982 Formula One world champion Keke, is already the youngest person to drive an F1 car after testing for Williams in 2002.
"I'm really looking forward to starting work at the end of this month and learning as much as I can," he said.
"I have always wanted to become an F1 driver and be a great F1 driver."
Rosberg had been vying with Antonio Pizzonia for the Williams seat made vacant by Jenson Button, who bought his way out of his contract in order to stay with BAR.
Team boss Frank Williams said: "I believe I am only one of many in Formula One who is genuinely excited about the prospect of Nico Rosberg.
"Given the attention he commands, I am delighted he is making a contribution to Formula One history and has signed with us for next season.
"His natural talent in the cockpit is equally matched by his intelligence out of it, demonstrated by his depth of technical understanding and communication of data over the months spent as a test driver this season."
Rosberg's Williams will be powered by Cosworth, the same combination that guided his Finnish father to the world championship 24 years ago.
Keke won five grands prix in 114 starts, a feat his son is hoping to eclipse.
"I hope I can top that count and I'm going to work very hard to be as good as he was, although I don't really want to compare myself to him," said Nico.
"But maybe I can compare to his achievements, because he has achieved the top in motorsports and that's my dream too. I'll work my very best to get there."
Rosberg admitted he faced a tough obstacle matching team-mate Webber.
"I have a team-mate who is very, very quick I think," he said. "Mark, especially on one lap, is one of the quickest in F1.
"I'm going to be able to learn a lot from him and I'm going to try and go out and be level with him on speed or even beat him."
Rosberg will debut in the Cosworth V8-powered Williams in testing at Barcelona on 29 November.